Insertion instrument for cervical prostheses

ABSTRACT

Insertion instrument for a multi-part intervertebral endoprosthesis ( 9 ) which comprises two closure plates ( 91, 92 ) and a sliding core ( 93 ) arranged between these, said insertion instrument having a handgrip part ( 21, 31 ), gripping members which hold the closure plates between them, and a force-receiving part for applying an insertion force to the intervertebral endoprosthesis ( 9 ), the gripping members being guided movably toward and away from one another via a hinge ( 4 ) and being able to be tensioned against the intervertebral endoprosthesis ( 9 ), projections ( 51, 52 ) pointing in the tensioning direction ( 12 ) or recesses for holding the intervertebral endoprosthesis ( 9 ) with form-fit being provided on the gripping members, and a block ( 61 ) guided in the longitudinal axis direction ( 10 ) and with an abutment surface ( 62 ) being provided which can be moved by means of an actuating device ( 7 ) so as to bear on the intervertebral endoprosthesis ( 9 ) and, in its forward position, secures the intervertebral endoprosthesis ( 9 ) against the projections ( 51 52 ) or recesses.

The invention relates to an insertion instrument for a multi-partintervertebral endoprosthesis which comprises two closure plates and asliding core arranged between these, said insertion instrument having ahandgrip part, gripping members which hold the closure plates betweenthem, and a force-receiving part for applying an insertion force to theintervertebral endoprosthesis.

For inserting intervertebral prostheses, an insertion instrument isknown (EP-A-1 306 064) which, at its front end, has two prosthesisholders for receiving in each case a prosthesis plate and which consistof two gripping members which are connected rigidly to one another andwhich hold the plates between them by friction. For very small implants,of the kind which are used in the area of the cervical spine and whichhave to be positioned very precisely, this may be too unreliable.

The object of the invention is to make available an improved instrumentfor implantation of intervertebral prostheses which is adapted inparticular to the requirements of implantation in confined conditions,as apply in particular in the area of the cervical spine.

The solution according to the invention lies in an insertion instrumentwith the features of claim 1. Advantageous developments are the subjectof the dependent claims.

In the case of an insertion instrument for a multi-part intervertebralendoprosthesis, in particular a cervical prosthesis, which comprises twoclosure plates and a sliding core arranged between these, said insertioninstrument having a handgrip part, gripping members which hold theclosure plates between them, and a force-receiving part for applying aninsertion force to the intervertebral endoprosthesis, the inventionprovides that the gripping members are guided movably toward and awayfrom one another via a hinge and are able to be tensioned against theintervertebral endoprosthesis, projections pointing in the tensioningdirection or recesses for holding the intervertebral endoprosthesis witha form-fit are formed on the gripping members, and a block guided in thelongitudinal axis direction and with an abutment surface is providedwhich can be moved to the intervertebral endoprosthesis by means of anactuating device and, in its forward position, secures theintervertebral endoprosthesis against the projections or recesses. Whenthe forceps-like insertion instrument is closed, the gripping membersconnected to one another via a hinge move toward one another and engagewith a form-fit via their projections (or recesses) in correspondingdepressions (or elevations) of the intervertebral endoprosthesis andthus tension the latter in a direction transverse to the longitudinalaxis of the insertion instrument. The longitudinally movably guidedblock can be moved toward the intervertebral endoprosthesis until itsabutment surface bears on the intervertebral endoprosthesis and securesthe latter against the projections (or recesses). In this way, theintervertebral endoprosthesis is also tensioned in the longitudinaldirection. It is thus held by the insertion instrument in a manner freeof play and in a precise position. By virtue of the block bearing firmlyon the intervertebral endoprosthesis, considerable forces, such as arisewhen striking the intervertebral endoprosthesis into place, can also besafely transmitted. Since these considerable forces are transmitted viathe block and its abutment surface, the projections (or recesses) do nothave to take up these forces. They can be of fairly small dimension andtherefore made very fine, as is desired for precise positioning, withouthaving to take into consideration the high force transmission whenstriking the intervertebral endoprosthesis home. In addition, by bearingon the intervertebral endoprosthesis, the block ensures that the latterdoes not inadvertently turn and that its individual elements do notopen. By virtue of the invention, the intervertebral endoprosthesis canthus be held easily, safely and with precise positioning on theinsertion instrument and inserted.

A number of terms are explained below:

The longitudinal axis of the forceps is understood as the center linewhich is the angle bisector between the handgrip parts of the forcepshalves and the jaw parts of the forceps halves.

The tensioning direction is understood as the direction in which thegripping members move toward one another. The opposite direction is thespreading direction. These directions are generally approximatelytransverse to the longitudinal axis of the insertion instrument.

A form-fit hold is understood as meaning that the projections engage incorrespondingly shaped receiving openings of the intervertebralendoprosthesis, or vice versa. Viewed in the direction of thelongitudinal axis, the projections grip into an undercut.

The insertion instrument is preferably designed as a forceps, whose jawparts form the gripping members. This permits a space-savingconstruction and easy handling, which is of advantage particularly inthe confined conditions in the area of the cervical spine.

To make it simpler to use, the actuating device has a rod with a handlearranged in the rear area of the handgrip part. This allows theoperating surgeon to use the actuating device without awkwardmaneuvering. Because of the small space available in the case ofcervical prostheses, this is of particular importance when removing theinsertion instrument after introduction of the intervertebralendoprosthesis, when the block has to be moved back. For this purpose,the rod is expediently provided with a screw thread and is guided in acounterthread which is fixed on the instrument and arranged preferablyin the hinge. Thus, by turning in one direction, the block can be guidedtoward the intervertebral endoprosthesis and thus secure it, whereas, byturning in the opposite direction, the block is moved away and releasesthe intervertebral endoprosthesis for the purpose of removal of theinsertion instrument. The screw device also has the advantage of beingself-locking, with the result that a separate securing device forprotection against inadvertent displacement is not necessary. However, ascrew device is not absolutely necessary, and, instead, other preferablyself-locking actuating devices can also be provided.

In a particularly advantageous construction, the actuating device isguided through the hinge. This is not only a particularly space-savingdesign, it also guarantees a near-center arrangement. This arrangementensures that the insertion instrument does not deviate to the side evenunder high forces when struck. A high degree of positioning precisionwhen inserting the intervertebral endoprosthesis is achieved in thisway.

It is expedient for the actuating device to have a strike head at itshandgrip end. In this way, via the actuating device and the block, it ispossible to act directly on the intervertebral endoprosthesis so as tobring it to its implantation site. For this purpose, it is expedient forthe handle itself to be designed as a strike head. This permits aspace-saving construction, which is of considerable value particularlyin the confined conditions in the area of the cervical spine.

In order to ensure that the insertion instrument does not inadvertentlyspring open, even when acted upon by considerable force, a lockingdevice is expediently provided for securing the handgrip parts in theposition when pressed together, said locking device having a guide forthe actuating device. This ensures that the actuating device does notdeflect outward under high loads, particularly when the strike head isarranged far to the rear. The locking device can be provided at the rearend of the handgrip parts in a manner known per se. It is important thatit is sufficiently strongly dimensioned to withstand the loads whichoccur during striking but can nevertheless be easily released forremoving the instrument.

In an expedient embodiment, the projections or recesses are arranged onjaw inserts which are fastened releasably on the jaw parts. This meansthat, if necessary, it is easy to exchange the jaw inserts together withthe projections or recesses arranged thereon, in order to adapt theinsertion instrument to other types or sizes of intervertebralendoprostheses.

The invention is explained below with reference to the drawing in whichan advantageous illustrative embodiment is shown, and where:

FIG. 1 shows an overall view of the insertion instrument according tothe invention, seen from above, with an intervertebral endoprosthesis;

FIG. 2 shows an overall view of the insertion instrument according tothe invention seen from below;

FIG. 3 shows an enlarged detail view of a jaw part of the insertioninstrument, in a longitudinal axis section;

FIG. 4 shows a detail view of the other jaw insert; and

FIG. 5 shows a detail view of the insertion instrument with anintervertebral endoprosthesis arranged thereon.

The illustrative embodiment, shown in the figures, of an insertioninstrument according to the invention is a forceps, labeled as a wholeby reference number 1. It is used for inserting cervical prostheses 9into the intervertebral space of two adjacent vertebral bodies of thecervical spine (not shown).

The forceps 1 is made up of two forceps halves 2, 3 which are connectedto one another movably via a pivot hinge 4. In their rear area, theforceps halves 2, 3 have a respective handgrip part 21, 31 and in theirfront area they have a respective jaw part 22, 32. The pivot hinge 4 isarranged at the transition between the handgrip parts 21, 31 and the jawparts 22, 32. It is formed by a pin 42 on the forceps half 2 (in FIG. 1it extends upward from the plane of the drawing), which pin 42 ismounted in a matching opening 43 in the central area of the otherforceps half 3. The bearing pin 42 has a through-bore 44 which runs fromthe handgrip area of the forceps halves 2, 3 to the jaw area. It will bediscussed in more detail later. The pivot hinge 4 allows the handgripparts 21, 31 of the forceps halves 2, 3 to be moved toward one anotherso that the jaw parts 22, 32 close, and vice versa.

The jaw parts 22, 32 function as gripping members. In the front area, ontheir mutually facing inner surfaces, they each have two projections 51,52 pointing in the tensioning direction 12. These projections are notarranged directly on the jaw parts 22, 32, but instead on jaw inserts 53which are secured exchangeably, by means of a screw (not shown), in acorresponding recess on the outer surfaces of the jaw parts 22, 32. Eachjaw insert 53 has a projection 51 and a projection 52. The projection 51is formed like a pin and is located in the upper area of the jaw insert53, while the projection 52 is formed like a small plate and is locatedin the lower area of the jaw insert 53. The dimensions and arrangementof the projections 51, 52 are adapted to corresponding receivingopenings on the cervical prostheses 9 to be received. This will beexplained in more detail later.

Arranged on the jaw part 22 there is a guide rail 60 which holds a block61 such that the latter is longitudinally displaceable in the forwardand rearward directions on the forceps half 2. The guide rail 60 isdesigned as an elongate hole in the jaw insert 53 of the jaw part 32. Agrub screw arranged laterally in the block 61 engages in the oblong holeforming the guide rail 60 and guides the block in the longitudinaldirection. Instead of the oblong hole, other guide elements can also beprovided which allow the block 61 to be guided in forward and rearwardmovement in the longitudinal direction, for example a dovetail guide. Atits front end, the block 61 is provided with an abutment surface 62designed to cooperate with the cervical prosthesis 9.

The block 61 is engaged by an actuating device 7 which extends from therear area of the block 61 via the through-bore 44 and into the areabetween the handgrip parts 21, 31. The actuating device 7 comprises acoupling element 70 for connection to the block 61, which, in theillustrative embodiment shown, is a vertebra support suitable fortransmitting shear forces, and it moreover comprises a rod 71 and ahandle 72 for actuation. Provided in the front area of the rod 71 thereis an external thread 73 which cooperates with a complementary internalthread (not shown) in the through-bore 44 of the pin 42 as aninstrument-fixed guide. By turning the handle 72, it is thus possiblefor the rod 71, and with it the block 61 via the coupling element 70, tobe moved backward and forward along the guide rail 60. The handle 72 isdesigned as a rotatable knob which, on its outer circumference 74, has asuitable surface finish, for example a coarse ribbing 75, to allow theoperating surgeon a good grip.

The rear end of the handle 72 is provided with a convex bulge 76. Itserves as a strike head for the actuating device 7. Impulses acting onthe bulge 76 of the strike head are transmitted by this via the rod 71of the actuating device 7, the shear-resistant vertebral support 70 andthe block 61, to the latter's abutment surface 62.

A locking device 8 for the handgrip parts 21, 31 is provided in the reararea of the forceps 1. This locking device 8 comprises a pivotablymovable catch element 83 and a locking pawl 84 (which are arrangedopposite one another on the handgrip parts 21, 31), a release device 81,a base 82 and a spring 87. The rear end of the handgrip part 21 isdesigned as a fork, the locking pawl 84 being formed by a beveling ofthe base of the fork. The catch element 83 is mounted by the base 82 inthe plane enclosed by the handgrip parts 21, 31. The spring 87 isdesigned as a leaf spring and acts on that end of the catch element 83mounted in the base 82 in such a way that it is pressed forward to thelocking pawl 84. Starting from the base 82, the catch element 83 has awide area and a narrow area. In its narrow area, the catch element 83has, on its front face, a toothing 86 into which, when the forceps 1 isclosed, the locking pawl 84 engages and is locked, so that the handgripparts 21, 31 cannot move away from one another and, as a result, theinsertion instrument 1 is safeguarded against inadvertently springingopen. In this way, it is possible for even substantial loads, forexample hammer strikes, to be applied to the bulge 76 on the forceps 1without any fear of inadvertent opening and without the operatingsurgeon needing to secure the handgrip parts 21, 31 by manual forceagainst undesired opening. To open the forceps 1 after implantation hasbeen carried out, the catch element 83 is pivoted rearward by applyingrearward pressure on the release element 81, by which means the lockingpawl 84 is freed from the catch element 83, and the handgrip parts 21,31 thus move apart from one another under the action of the spring 11.With the forceps 1 in the opened state, the catch element 83 is pivotedrearward counter to the force of the spring 87. Provided in the widearea of the catch element 83 there is a guide 85 which is designed as anoblong hole and which is used to hold the rod 71, even when the forceps1 is open, in a defined position in the longitudinal axis 10 and toavoid deflection of the rod 71 even under high loads.

Also fixed on the handgrip part 31 there is a leaf spring 11 which isguided round the rod 71 to the other handgrip part 21. With the forceps1 closed, this leaf spring 11 is tensioned and has the effect that,after release of the catch elements 82 83, the insertion instrument 1automatically opens to permit removal.

The cooperation with the cervical prosthesis 9 will be described nowwith reference to FIGS. 3 and 5. The cervical prosthesis 9 consists ofan upper closure plate 91 and a lower closure plate 92, with a pivot[sic] element 93 arranged between them. The cervical prosthesis 9 isintended for implantation in the interspace between two adjacentvertebrae of a human cervical spine. The top closure plate 91 is securedto the upper vertebra and the bottom closure pate 92 is secured to thelower vertebra. To arrange the cervical prosthesis 9 securely on theforceps 1 for insertion into the intervertebral space, the top andbottom closure plates 91, 92 have receiving openings on their lateralflanks in the area of their front flange 94, 95. The receiving openingon the top closure plate 91 is designed as a bore 97 with an additionalcountersink. The receiving opening on the bottom closure plate 92 isdesigned as a slit 96. In its flange-side area, the sliding core 93 islikewise provided with a slit 96′ which is arranged in such a way thatit is flush with the slit 96 of the bottom closure plate 92. The slits96, 96′ thus result in a continuous groove.

To receive the cervical prosthesis 9 with the forceps 1, the cervicalprosthesis 9 is brought into the area between the jaw parts 22, 32 andthe forceps 1 is closed, as a result of which the jaw parts 22, 32 movetoward one another. In so doing, the projections 51, 52 engage in thecorresponding receiving openings of the two closure plates 91, 92, thepins 51 engaging in the bore 97 and the small plates 52 engaging in theslits 96, 96′. In this way, the cervical prosthesis 9, in the tensioningdirection, is held free from play on the forceps 1. The different designof the projections 51, 52 and of the receiving openings configured asbores 97 and slits 96 ensures that the cervical prosthesis 9 can be heldon the forceps 1 only with the correct orientation. If, as in theillustrated embodiment, the forceps 1 is additionally provided with amarking 14 for the top, this virtually eliminates the possibility ofincorrect implantation as a result of incorrect orientation of thecervical prosthesis 9. After the cervical prosthesis 9 has in this waybeen received in the correct orientation on the forceps 1, the rod 71can be moved forward via the actuating device 7 by turning the handle72, with the result that the block 61 comes to lie, from the rear, withits abutment surface 62 on the flange 94, 95 of the cervical prosthesis9. In doing so, the block 61 tensions the cervical prosthesis 9 againstthe projections 51, 52 and thus orients the cervical prosthesis 9 in adefined position. Any play existing in the longitudinal axis directionbetween the projections 51, 52 and the bores 97 and the slits 96 iscompensated in this way. The cervical prosthesis 9 is thus held securelyand in a precise position on the forceps 1. In addition, the fact thatthe block 61 bears on the flanges 93, 94 of the two closure plates 91,92 ensures that the two closure plates 91, 92 do not move away from oneanother at their front end. This eliminates the possibility of thecervical prosthesis 9 opening, which would prevent successfulintroduction into the intervertebral space.

It is furthermore made possible to implant cervical prostheses ofdifferent height without making changes to the forceps 1. FIG. 3 b showsa cervical prosthesis 9′ which has a thicker sliding core 93′. Like thesliding core 93, it is provided with a slit 96″ which is flush with theslit 96 of the bottom closure plate 92. This configuration of thereceiving opening on the bottom closure plate 92 as a slit 96 and itscontinuation as slit 96″ in the sliding core 93′ ensure that the thickercervical prosthesis 9′ can be gripped and securely held with the sameforceps 1 without changing the arrangement of the projections 51, 52.The positioning precision is in this case guaranteed by the pin-likeprojections 51 which engage in the bores 97.

If necessary, however, it is also possible to provide other jaw inserts53′ which have a different arrangement of the projections 51′, 52′, asis shown in FIG. 4. In this way, the forceps 1 can be adapted to otherintervertebral endoprostheses, for example to particularly small onesfor treatment of children.

With its abutment surface 62, the block 61 affords a sufficiently largeforce transmission surface for transmitting to the cervical prosthesis 9the impulses applied to the bulge 76 acting as the strike head. Thegreat advantage of this is that the projections 51, 52, which have beenfinely dimensioned in the interest of precise positioning, do not haveto transmit the strike forces, so that the risk of bending or evenbreaking of the projections 51, 52 as a result of overloading isexcluded, by virtue of the block 61 and its abutment surface 62 assumingthe role of force transmission.

The forceps 1 according to the invention allows the cervical prosthesis9 to be arranged with precise positioning and without any risk of itsbeing the wrong way round on the forceps 1, thereby preventing anyundesired opening of the cervical prosthesis 9. Moreover, by virtue ofthe block 61 with the abutment surface 62, it also permits transmissionof forces even in the case of forceps 1 of small dimensions. In thisway, reliable implantation of the prosthesis is guaranteed. The smalldimensioning of the forceps 1 also has the advantage that it gives theoperating surgeon good access to and a good overall view of theimplantation site.

1. An insertion instrument for a multi-part intervertebralendoprosthesis comprising: two closure plates and a sliding corearranged between the closure plates, an insertion instrument comprisinga handgrip part, gripping members which hold the closure plates betweenthem a hinge, a force-receiving part for applying an insertion force tothe intervertebral endoprosthesis, projections pointing in a tensioningdirection or recesses for holding the intervertebral endoprosthesis witha form-fit formed on the gripping members, and a block guided in thelongitudinal axis direction and provided with an abutment surface (62)is provided which configured to be movable by an actuating device so asto bear on the intervertebral endoprosthesis and, in a forward position,so as to secure the intervertebral endoprosthesis against theprojections or recesses, wherein the gripping members are configured tobe guided movably toward and away from one another via the hinge and tobe tensioned against the intervertebral endoprosthesis.
 2. The insertioninstrument according to claim 1, wherein the insertion instrument isdesigned as a forceps, whose jaw parts form the gripping parts. 3.Insertion The insertion instrument according to claim 1 or 2, whereinthe actuating device is a rod with a handle arranged in the rear area ofthe handgrip part.
 4. The insertion instrument according to claim 3,wherein the rod is provided with a screw thread and is guided in acounter thread which is fixed on the instrument and arranged in thehinge.
 5. The insertion instrument according to claim 2, wherein theactuating device is guided through the hinge.
 6. The insertioninstrument according to claim 1 or 2, wherein the handle is designed asa strike head.
 7. The insertion instrument according to claim 1 or 2,further comprising a locking device provided for securing the handgripparts in the position when pressed together, the locking device having aguide for the actuating device.
 8. The insertion instrument according toclaim 1 or 2, wherein the projections are arranged on jaw inserts whichare fastened releasably on the jaw parts.
 9. The insertion instrumentaccording to claim 7, wherein the actuating device is a rod with ahandle arranged in the rear area of the handgrip part.
 10. The insertioninstrument according to claim 8, wherein the actuating device is a rodwith a handle arranged in the rear area of the handgrip part.
 11. Theinsertion instrument according to claim 4, further comprising a lockingdevice provided for securing the handgrip parts in the position whenpressed together, the locking device having a guide for the actuatingdevice.
 12. The insertion instrument according to claim 8, furthercomprising a locking device provided for securing the handgrip parts inthe position when pressed together, the locking device having a guidefor the actuating device.